12-year-old Alice and her best mate Tarun are Peppercorns, detectives who are used to solving tricky mysteries. They are spending the summer holidays together on a boat where Jaswinder, Tarun's mother, works on a top-secret maritime research project. But what looks to be a relaxing summer turns out to be quite the opposite. One day, important research is stolen from Jaswinder, and then she vanishes without a trace. Alice and Tarun have to find the culprit.
Aided by their newfound friends, Clarissa and her brother Jonny, and the leader of the local kids' gang, Hanna, they begin their investigation. To find out what happened to Jaswinder they have to confront powerful and dangerous people. But who can the Peppercorns trust?